Elastomeric layer fabrication for light emitting diodes

ABSTRACT

An elastomeric interface layer (elayer) is formed over multiple light emitting diode (LED) dies by depositing photoresist materials across multiple LED dies, and using the LED dies as a photolithography mask to facilitate formation of the elayer on each LED die. The elayer facilitates adhesive attachment of each LED die with a pick and place head (PPH), allowing the LED dies to be picked up and placed onto a display substrate including control circuits for sub-pixels of an electronic display. In some embodiments, the LED dies are micro-LED (μLED) dies.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/789,275, filed Oct. 20, 2017, which is incorporated by reference inits entirety.

BACKGROUND

The present disclosure relates to semiconductor device fabrication,specifically to placing a conformable material over light emitting diode(LED) dies to facilitate adhesive attachment in display fabrication.

In LED display fabrication, LEDs may be moved from one substrate toanother. That is, micro-LEDs of different color may be transferred fromsource substrates where the micro-LEDs were fabricated onto carriersubstrates, and then from carrier substrates onto a display substrateincluding control circuits for controlling the micro-LEDs. Transferringthe micro-LEDs from the carrier substrates onto the display substratemay involve picking and placing of LEDs onto desired locations on thedisplay substrate. As the form factor of LED's decreases, the pickingand placing of LEDs into desired arrangements and without damaging theLED dies becomes increasingly difficult.

SUMMARY

Embodiments relate to forming an elastomeric interface layer (elayer)over multiple light emitting diode (LED) dies by depositing photoresistmaterials across multiple LED dies, and using the LED dies as aphotolithography mask to facilitate formation of the elayer on each LEDdie. The elayers facilitate adhesion with a pick-up head for pick andplace operation during the manufacturing of an electronic display.

In some embodiments, a photoresist material on and between lightemitting diode (LED) dies is deposited on a carrier substrate. Thephotoresist material may be a negative photoresist material that becomesinsoluble when exposed to light. After depositing the photoresistmaterial, light is applied through the carrier substrate towards the LEDdies and the deposited photoresist material. A portion of the lightincident on the LED dies is absorbed by the LED dies to retain solublefirst portions of the photoresist material on the LED dies. Otherportions of photoresist material between the LED dies are exposed to thelight, causing second portions of the photoresist material between theLED dies to become insoluble. After applying the light, the solublefirst portions of photoresist material on the LED dies are removed, suchas by dissolving in a photoresist developer. After removing the firstportions of the photoresist material on the LED dies, an elastomericmaterial is deposited on each LED die and between the second portions ofphotoresist. The second portions of the photoresist material are removedafter depositing the elastomeric material. The elastomeric materialremaining on the LED dies forms elastomeric interface layers on the LEDdies to facilitate adhesion with a pick and place head (PPH) (or a“pick-up head”).

In some embodiments, at least a portion of the LED dies on the carriersubstrate can be picked up by attaching a non-conformable pick-up headto the elastomeric interface layers over the LED dies. At least aportion of the LED dies attached to the non-conformable pick-up head areplaced on a display substrate defining pixel control circuits of anelectronic display.

In some embodiments, the first portions of photoresist material areremoved by dissolving the first portions with a first solvent. The firstsolvent may be a photoresist developer. The second portions of thephotoresist material are used as molds for forming the elastomericlayers, and then removed, such as by dissolving the second portions ofthe photoresist material with a second solvent different from the firstsolvent, such as a photoresist stripping material that removes insolublephotoresist material. The first solvent is benign to the second portionsof the photoresist material, and the second solvent is benign to theelastomeric material forming the elastomeric interface layers on the LEDdies. In some embodiments, the second portions of photoresist materialare removed by applying light to cause the second portions to becomesoluble, and then dissolving the second portions using the same solventused in dissolving the first portions of photoresist material.

In some embodiments, the LED dies are micro-LED (mLED) dies. In someembodiments, an elastomeric interface layer is formed over multiplevertical-cavity surface-emitting lasers (VCSELs), or other types ofLEDs. In some embodiments, the LED dies include Gallium nitride (GaN),gallium arsenide (GaAs), or gallium phosphide (GaP). In someembodiments, the LED dies absorb Ultraviolet (UV) light incident on theLED dies through the carrier substrate.

In some embodiments, an electronic display panel is fabricated. Aphotoresist material is deposited on and between light emitting diode(LED) dies on a carrier substrate. Light is applied through the carriersubstrate towards the LED dies and the deposited photoresist material,responsive to depositing the photoresist material. A portion of thelight incident on the LED dies is absorbed by the LED dies to retainsoluble first portions of the photoresist material on the LED dies.Other portions of photoresist material between the LED dies are exposedto the light to render second portions of the photoresist materialbetween the LED insoluble. The first portions of photoresist materialare removed, responsive to applying the light, such as by dissolvingwith a photoresist developer. An elastomeric material is deposited oneach LED die and between the second portions of photoresist, responsiveto removing the first portions. The second portions of the photoresistmaterial are removed responsive to depositing the elastomeric material,the elastomeric material forming elastomeric interface layers on the LEDdies. At least a portion of the LED dies are picked up on the carriersubstrate by attaching a non-conformable pick-up head to the elastomericinterface layers over the LED dies. The at least a portion of the LEDdies attached to the non-conformable pick-up head are placed on adisplay substrate defining pixel control circuits of an electronicdisplay.

Some embodiments include using a positive photoresist material that isalso an elastomeric material to form elastomeric interface layers on theLED dies. A photoresist material is deposited on and between LED dies ona carrier substrate. Light is applied through the carrier substratetowards the LED dies and the photoresist material. A portion of thelight incident on the LED dies is absorbed to retain insoluble firstportions of the photoresist material on the LED dies insoluble. Secondportions of the photoresist material between the LED dies are exposed toanother portion of the light to render the second portions soluble.Here, the photoresist material may be a positive photoresist thatbecomes soluble when exposed to the light. The soluble second portionsof the photoresist material are removed, and the first portions of thephotoresist material are retained to form elastomeric interface layerson the LED dies. In some embodiments, the second portions of thephotoresist material are removed by dissolving the second portions witha solvent.

In some embodiments, an electronic display panel is fabricated. Aphotoresist material is deposited on and between light emitting diode(LED) dies on a carrier substrate. Light is applied through the carriersubstrate towards the LED dies and the photoresist material, responsiveto depositing the photoresist material. A portion of the light incidenton the LED dies is absorbed to retain insoluble first portions of thephotoresist material on the LED dies. Second portions of the photoresistmaterial between the LED dies are exposed to another portion of thelight to render the second portions soluble. The second portions of thephotoresist material are removed but the first portions of thephotoresist material remain to form an elastomeric interface layer onthe LED dies. At least a portion of the LED dies on the carriersubstrate are picked up by attaching a non-conformable pick-up head tothe elastomeric interface layers over the LED dies. The at least aportion of the LED dies attached to the non-conformable pick-up head areplaced on a display substrate defining pixel control circuits of anelectronic display.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view of LED dies on a carrier substrate withan elastomeric interface layer (elayer) over each LED die, according toone embodiment.

FIG. 2 is a flowchart of a method for forming an elayer over LED dies onthe carrier substrate, with a negative photoresist material, accordingto one embodiment.

FIG. 3 is a cross sectional view of LED dies on the carrier substrate,according to one embodiment.

FIG. 4 is a cross sectional view of LED dies on the carrier substratewith negative photoresist material on and between the LED dies,according to one embodiment.

FIG. 5 is a cross sectional view of the LED dies, with the addition ofapplied light, according to one embodiment.

FIG. 6 is a cross sectional view of the LED dies on the carriersubstrate with portions of soluble photoresist material and insolublephotoresist material caused by the applied light, according to oneembodiment.

FIG. 7 is a cross sectional view of the LED dies with the portions ofsoluble photoresist material removed, according to one embodiment.

FIG. 8 is a cross sectional view of the LED dies including elastomericmaterial, according to one embodiment.

FIG. 9 is a flowchart of a method for forming an elayer over LED dies onthe carrier substrate, with a positive photoresist material, accordingto one embodiment.

FIG. 10 is a cross sectional view of LED dies on the carrier substratewith positive photoresist material on and between the LED dies,according to one embodiment.

FIG. 11 is a cross sectional view of the LED dies with applied light,according to one embodiment.

FIG. 12 is a cross sectional view of LED dies on the carrier substratewith portions of soluble photoresist material and other portions ofinsoluble photoresist material that forms elayers on the LED dies,according to one embodiment.

FIG. 13 is a display manufacturing system during pick up of LED diesfrom a carrier substrate, according to one embodiment.

FIG. 14 is a display manufacturing system during placement of LED dieson a display substrate, according to one embodiment.

FIG. 15 is a schematic diagram of a cross section of a micro-LED,according to one embodiment.

The figures depict various embodiments of the present disclosure forpurposes of illustration only. One skilled in the art will readilyrecognize from the following discussion that alternative embodiments ofthe structures and methods illustrated herein may be employed withoutdeparting from the principles of the disclosure described herein.

DETAILED DESCRIPTION

In the following description of embodiments, numerous specific detailsare set forth in order to provide more thorough understanding. However,note that the embodiments may be practiced without one or more of thesespecific details. In other instances, well-known features have not beendescribed in detail to avoid unnecessarily complicating the description.

Embodiments are described herein with reference to the figures, wherelike reference numbers indicate identical or functionally similarelements. Also in the figures, the left most digits of each referencenumber corresponds to the figure in which the reference number is firstused.

Embodiments relate to depositing an elastomeric interface layer (elayer)over multiple light emitting diode (LED) dies by using photoresistmaterials rather than physical molds or processes that may damage theelayer or the LED dies. The deposited elayer allows each LED to bepicked up by a pick-up head (or pick and place head (PPH)), and placedonto a display substrate including control circuits for sub-pixels of anelectronic display. In some embodiments, the LED dies are micro-LED(mLED) dies.

FIG. 1 is a cross sectional view of LED dies 102 on a carrier substrate104 with an elastomeric interface layer (elayer) 110 over each LED die102, according to one embodiment. The LED dies 102 may be fabricated ona source substrate and placed onto the carrier substrate 104 tofacilitate pick and place onto a display substrate of an electronicdisplay. The carrier substrate 104 may include a substrate 106 on whichthe LED dies 102 are placed, and an adhesive layer 108 that holds theLED dies 102 on the substrate 106.

The elayer 110 is formed on the light emitting side 112 of each LED die102. The elayer 110 is a conformable layer that allows each of the LEDdies 102 to be attached to and picked up by a pick and place head (PPH)(e.g., as discussed in greater detail with reference to FIG. 13). Inparticular, the elayer 110 facilitates attachment with non-conformablepick-up surfaces 1304 of the PPH 1302, or in another example,conformable pick-up surfaces 1304 of a PPH 1302. The elayer 110 mayattach to a pick-up surface 1304 due to adhesion forces, such as Van derWaals. The elayer 110 may include any material that provides sufficientadhesion to the pick-up surfaces 1304. For example, the elayer 110includes elastomers, such as Polydimethylsiloxane (PDMS) or Polyurethane(PU). In some embodiments, the interface layer on the light emittingside 112 of the LED dies 102 contains no elastomeric materials. Forexample, the elayer 110 includes gels that provides adhesion viacovalent chemical bonds. The elayer 110 may be polymer withviscoelasticity (having both viscosity and elasticity). The elayer 110may also include materials that have weak inter-molecular forces, a lowYoung's modulus, and/or high failure strain compared with othermaterials.

The side of each LED die 102 facing the carrier substrate 104 includescontact pads 114. Each of the LED dies 102 emit light out of the lightemitting side 112 if an electric potential is applied between electricalcontact pads 114. The electrical contact pads 114 connect with controlcircuits in a display substrate (e.g., as shown in FIG. 14) that drivethe LED dies 102 when the LED dies 102 are mounted to the displaysubstrate.

As discussed in greater detail below in connection with FIG. 15, the LEDdies 102 may be mLED dies including an epitaxial structure with gallium,such as gallium nitride (GaN), gallium arsenide (GaAs), or galliumphosphide (GaP). The gallium material of the LED dies may block certainwavelengths of light to serve as a mask for photoresist material used informing the elayer 110. In some embodiments, the method and principlesas described with reference to LED dies 102 can be applied to othersemiconductor or microelectronic devices. For example, an elayer may beformed on a vertical-cavity surface-emitting laser (VCSEL) to facilitatepick and place of the VCSEL.

The carrier substrate 104 has a flat surface mounted with LED dies 102that supports the LED dies 102 during the process of forming the elayer110 over each LED die 102. The carrier substrate 104 is transparent to,at least some, wavelengths of light. For example, the carrier substrate104 may include a glass or sapphire substrate that is transparent tolight that changes photoresist material state and is absorbed by the LEDdies 102. This allows light to be applied through the carrier substrate104 to the bottom sides of the LED dies 102 and the regions between theLED dies 102, resulting in photoresist material over LED dies 102 to beblocked from the light and exposing photoresist material between the LEDdies 102 to the light. The carrier substrate 104 may have any number ofLED dies 102 attached, such as one or more arrays of LED dies. Thecarrier substrate 104 may have a hard flat surface, rigid enough tosupport the LED dies 102 as the carrier substrate 104 is moved. In someembodiments, the LED dies 102 are released from the carrier substrate104 by removing the adhesive 108 (e.g., with a solvent, wet or dryetching, etc.), or weakening the adhesive 108. In other embodiments, theadhesive 108 is weak enough that the LED dies 102 may be removed withforce (e.g., by a PPH 1302) without damaging the LED dies 102.

FIG. 2 is a flowchart of a method 200 for forming an elayer 110 over LEDdies 102 on the carrier substrate 104, according to one embodiment.Specifically, a negative photoresist material provides a temporarytemplate for forming the elayer 110 that can be gently removed withoutdamaging the elayer 110 or LED dies 102. Among other advantages, themethod 200 provides for simultaneous formation of an elayer 110 onmultiple LED dies 102 without disturbing the positions of the LED dies102 or damaging the LED dies 102 or the elayers 110. The steps may beperformed in different orders, and the method 200 may include different,additional, or fewer steps. The method 200 is discussed with referenceto FIGS. 3 through 8, which show the formation of the elayer 110 on LEDdies 102.

A negative photoresist material is deposited 402 in the regions betweenthe LED dies 102 on the carrier substrate 104 and over the LED dies 102.With reference to FIG. 3, showing a cross sectional view of the LED dies102 on the carrier substrate 104, the LED dies 102 may be evenly spacedapart on the carrier substrate 104 and attached to the carrier substrate104 via a layer of adhesive 108. With reference to FIG. 4, showing across sectional view of the LED dies with negative photoresist material402, the negative photoresist material 402 is a light-sensitive materialthat is initially soluble and becomes insoluble when exposed to light.For example, without exposure to the light, the negative photoresistmaterial 402 can be removed with a solvent, such as a photoresistdeveloper. The negative photoresist material 402 can be mixed with asolvent such that the negative photoresist material 402 is viscous forplacement (e.g., via spin coating) onto the LED dies 102 and carriersubstrate 104, and then baked (e.g., soft baking) on the LED dies 102.

The carrier substrate 104 may be an intermediate substrate to facilitateLED die 102 transfer between a native substrate and the displaysubstrate 1402. The space between the LED dies 102 may be a result ofthe singulation process (in which a single group of LED dies 102 areseparated into individual LED dies 102) or another process that createsthe open regions between the LED dies 102.

For example, the open regions between the LED dies 102 may be formed bythe use of an expanding carrier film. The carrier film is attached to afirst side of the LED dies 102 on a native substrate. The LED dies 102may be singulated before or after the carrier film is attached to theLED dies 102. After the LED dies 102 are detached from the nativesubstrate, the LED dies 102 are separated by expanding the carrier filmto widen the open regions between the LED dies 102. The carriersubstrate 104 is applied to a second side of the LED dies 102. The LEDdies 102 are attached to the adhesive 108 layer of the carrier substrate104 with the open regions being defined between the LED dies 102. Thecarrier film is separated from the first side of the LED dies 102 toexpose the first die of the LED dies 102 for formation of the elayer110.

After depositing the negative photoresist material 402, light is applied204 through the carrier substrate 104 towards the LED dies 102 and thedeposited negative photoresist material 402. With reference to FIG. 5,showing a cross sectional view of the LED dies 102 with applied light502, the carrier substrate 104 is, at least partially, transparent tothe applied light 502. The transparent carrier substrate 104 allows thelight 502 to shine on portions of the negative photoresist material 402between the LED dies 102 that are not blocked by the LED dies 102. Byapplying light through the carrier substrate 104 and using the LED dies102 to block portions of the light 502, a separate photomask or maskingprocess to selectively block light from reaching portions of thenegative photoresist material 402 is not needed. In some embodiments,the light 502 is collimated ultraviolet (UV) light, and the carriersubstrate 104 includes glass or sapphire that is transparent to the UVlight 502, while the LED dies 102 include gallium or other material thatabsorbs the UV light 502. However, other wavelengths of light andmaterials may be used such that the substrate is transparent to thelight, the LED dies absorb the light, and the light changes the state ofthe photoresist.

Light 502 incident on the LED dies is absorbed 206 to retain solublefirst portions of the negative photoresist material 402 on the LED dies102. With reference to FIG. 6, showing a cross sectional view of the LEDdies 102 with soluble photoresist material 602 and insoluble photoresistmaterial 604, the light 502 is directed at the LED dies 102 is absorbedby the LED dies 102 so that the negative photoresist material 402 on topof the LED dies 102 is not exposed to the applied light 502 and remainssoluble photoresist material 602.

Portions of the negative photoresist material 402 between the LED dies102 are exposed 208 to light 502 to render the second portions of thenegative photoresist material 402 between the LED dies 102 insoluble.With reference to FIG. 6, insoluble photoresist material 604 is formedbetween the LED dies 102. Because the negative photoresist material 402is a negative resist, the light 502 renders the photoresist materialinsoluble, creating the insoluble photoresist material 604 between theLED dies 102. In some embodiments, the insoluble photoresist material604 can be insoluble to a first solvent, such as a photoresistdeveloper, but soluble to a second solvent, such as a photoresiststripper.

After applying the light 502, first portions of the negative photoresistmaterial 402 over the LED dies 102 are removed 210. With reference toFIG. 7, showing a cross sectional view of the LED dies 102 with solublephotoresist material 602 removed over the LED dies 102, the solublephotoresist material 602 is removed to expose the light emitting side112 of the LED dies 102. Since the first portions the negativephotoresist material 402 over the LED dies 102 were not exposed to thelight 502, the first portions are soluble photoresist material 602. Thesoluble photoresist material 602 is soluble to a solvent, such as aphotoresist developer like sodium or potassium carbonate solution. Thesolvent is a substance that reacts to remove the soluble photoresistmaterial 602 while being benign to the insoluble photoresist material604. For example, the solvent is a liquid that dissolves the solublephotoresist material 602.

Elastomeric material 802 is deposited 212 on each LED die 102 andbetween the second portions of insoluble photoresist material 604, afterremoving the first portions of soluble photoresist material 602. Withreference to FIG. 8, showing a cross sectional view of the LED dies 102with elastomeric material 802, the soluble photoresist material 602 isremoved resulting in the insoluble photoresist material 604 forming amold for the elastomeric material 802. The elastomeric material 802 isformed on the light emitting side 112 of the LED dies 102 between themold walls of the insoluble photoresist material 604. The elastomericmaterial 802 forms the elayer 110 over the LED dies. As discussed withreference to FIG. 1, the elastomeric material 802 which forms the elayer110 may include any material that provides sufficient adhesion to thepick-up surfaces 1304. In some embodiments, the elastomeric material 802is cured. The curing may harden the elastomeric material 802 andattaches the elastomeric material 802 on the LED dies 102 elastomericmaterial 802. The elastomeric material 802 may be cured in various ways,such as by application of light, heat, chemical additives, and/orvulcanization.

After depositing the elastomeric material 802, the second portions ofthe photoresist material (the insoluble photoresist material 604) areremoved 214, resulting in the elastomeric material 802 forming an elayer110 on each of LED dies 102. With reference to FIG. 1, separate elayers110 are on each of the LED dies 102, and the photoresist material usedin forming the elayers 110 is removed. The second portions of theinsoluble photoresist material 604 form a mold that can be removed in amanner that is benign to the elastomeric material 802. In someembodiments, the second portions of the insoluble photoresist material604 are removed after the elastomeric material 802 is cured. In otherembodiments, the elastomeric material 802 is cured after removal of theinsoluble photoresist material 604. In some embodiments, the insolublephotoresist material 604 can be removed with a solvent different fromthe solvent used to remove the soluble photoresist material 602. Forexample, the insoluble photoresist material 604 may be removed using aphotoresist stripping material for insoluble photoresist, such asacetone. In other embodiments, the negative photoresist material 402 isa reversible photoresist, such that the insoluble photoresist material604 is reversed (e.g., by application of light) to become solublephotoresist material, and then removed with a solvent developer (e.g.,the same solvent used to remove the first portions of photoresistmaterial. For example, laser light incident upon the insolublephotoresist material 604 may be used to render the material soluble. Inother embodiments, the insoluble photoresist material 604 is removed bydry etching, for example with an oxygen or air radio frequency (RF)plasma. After the insoluble photoresist material 604 is removed, theelastomeric material 802 forms an elayer 110. The elayer 110 isconformable layer that allows each of the LED dies 102 to be attached toand picked up by a pick-up surface 1304 of a pick and place head (PPH)1302.

FIG. 9 is a flowchart of a method 900 for forming an elayer 110 over LEDdies 102 on the carrier substrate 104, according to one embodiment. Themethod 900 includes a positive material that forms the elayer 110 overthe LED dies 102. Among other advantages, the method 900 provides forsimultaneous formation of an elayer 110 on multiple LED dies 102 withoutdisturbing the positions of the LED dies 102 or damaging the LED dies102 or the elayers 110. After forming the elayers 110, the method 900allows each LED die 102 to be picked up by a PPH 1302 and moved to adisplay substrate 1402 (e.g., as discussed in greater detail below withreference to FIGS. 13 and 14). The steps may be performed in differentorders, and the method 900 may include different, additional, or fewersteps. The method 900 is discussed with reference to FIGS. 10 through12, which show the formation of the elayer 110 on LED dies 102.

Positive photoresist material is deposited 902 in the regions betweenthe LED dies 102 on the carrier substrate 104 and over the LED dies 102.The LED dies 102 on the carrier substrate 104 may be evenly spaced apartand mounted to the substrate 106 by a layer of adhesive 108 (e.g., asshown in FIG. 3). With reference to FIG. 10, showing a cross sectionalview of the LED dies 102 with positive photoresist material 1002, thepositive photoresist material 1002 is a light-sensitive material that isinitially insoluble and becomes soluble when exposed to light. Forexample, after exposure to light, the positive photoresist material 1002can be removed with a solvent, such as a photoresist developer. Thepositive photoresist material 1002 can be mixed with a solvent such thatthe material is viscous for placement (e.g., via spin coating), and thenbaked (e.g., soft baking) on the LED dies 102.

The positive photoresist material 1002 eventually forms an elayer 110over the LED dies 102. In some embodiments, the positive photoresistmaterial 1002 includes materials to increase adhesion to the pick-upsurfaces 1304. For example, the positive photoresist material 1002 ismixed with a functional group material which is able to bind (e.g.,covalently) to the non-conformable pick-up surface 1304. In someembodiments, the elastomeric material is cured in connection with bakingthe positive photoresist material 1002. In other embodiments, a separatecuring process is used to cure the elastomeric material.

After depositing the positive photoresist material 1002, light isapplied 904 through the carrier substrate 104 towards the LED dies 102and the positive photoresist material 1002. With reference to FIG. 11,showing a cross sectional view of the LED dies 102 with applied light502, the carrier substrate 104 is, at least partially, transparent tothe applied light 502. The transparent carrier substrate 104 allows thelight 502 to shine on portions of the positive photoresist material 1002that are not blocked by the LED dies 102. One advantage of method 900 isthat a photomask and masking process is not required to selectivelyblock light from reaching portions of the positive photoresist material1002 over the LED dies 102. In some embodiments, the light 502 iscollimated ultraviolet (UV) light, such that the carrier substrate 104is transparent to the UV light 502, while the LED dies 102 absorb the UVlight 502.

Portions of the light 502 incident on the LED dies 102 are absorbed 906to retain insoluble first portions of the positive photoresist material1002 on the LED dies 102. With reference to FIG. 12, showing a crosssectional view of the LED dies 102 including insoluble photoresistmaterial 1202 and soluble photoresist material 1204, the light 502 isabsorbed by the LED dies 102 so that the positive photoresist material1002 on top of the LED dies 102 is not exposed to the applied light 502and remains insoluble photoresist material 1202.

Second portions of the photoresist material between the LED dies 102 areexposed 908 to another portion of light 502 to render the secondportions soluble. The light 502 renders the portions of the positivephotoresist material 1002 soluble, forming the soluble photoresistmaterial 1204 between the LED dies 102.

The second portions of the photoresist material (the soluble photoresistmaterial 1204) are removed 910, to form an elayer 110 on each of the LEDdies 102, from the first portions of the insoluble photoresist material1202. The soluble photoresist material 1204 can be removed with asolvent. The solvent may be a photoresist developer that dissolvessoluble photoresist material 1204, but is benign to insolublephotoresist material 1202. The remaining insoluble photoresist material1202 forms the elayers 110 on the LED dies 102. The elayer 110 isconformable layer that allows each of the LED dies 102 to be attached toand picked up by a pick-up surface 1304 of a pick and place head (PPH)1302. In some embodiments, the insoluble photoresist material 1202 iscured after removal of the soluble photoresist material 1204 to form theelayers 110.

FIG. 13 is a display manufacturing system 1300 during pick up of the LEDdies 102 from a carrier substrate 104, according to one embodiment. Thesystem 1300 includes a PPH 1302 for picking LED dies 102 from thecarrier substrate 104. The system 1300 includes the LED dies 102, thecarrier substrate 104, a micromanipulator 1306, a PPH 1302 defining anaxis 1308, and pick-up surfaces 1304. The LED dies 102 are mounted tothe carrier substrate 104. The micromanipulator 1306 moves the PPH 1302,such as with 6 degrees of freedom. The PPH 1302 includes pick-upsurfaces 1304 that adheres with the elayers 110 of the LED dies 102 forpick and place operations.

The micromanipulator 1306 is connected to the PPH 1302 and controlsmovement of the PPH 1302. The micromanipulator 1306 aligns the PPH 1302with the carrier substrate 104 to allow the PPH 1302 to pick up one ormore LED dies 102. In some embodiments, the micromanipulator 1306 may bea multiple degree of freedom micromanipulator, such as a four degree offreedom micromanipulator configured to move the PPH 1302 up and down,left and right, forward and back, or rotate the PPH 1302 (e.g., alongthe rotational axis 1308). In some embodiments, the system 1300 includesmultiple micromanipulators 1306 and/or PPHs 1302 to perform pick andplace tasks in parallel to increase throughput of the system.

The PPH 1302 has a polygon shaped cross section. The edges of thepolygon shape cross section define multiple pick-up surfaces 1304 of thePPH 1302. The elayer 110 of each LED dies 102 are configured to mount tothe pick-up surfaces 1304 (e.g., due to adhesion forces) to facilitatetransfer of the LED dies 102 from the carrier substrate 104 to a displaysubstrate 1402. The PPH 1302 may be rotated along the rotational axis1308 to pick up arrays of LED dies 102 at one or more pick-up surfaces1304. Although the PPH 1302 has an octagonal cross section and eightpick-up surfaces 1304, a PPH 1302 may have different shaped crosssections (e.g., triangular, square, hexagon, etc.) and different numbersof pick-up surfaces in various embodiments. Although the pick and placetool discussed herein is a PPH 1302, other types of pick-up heads usingadhesive attachment with elayers 110 may be used.

The pick-up surfaces 1304 may be non-conformable pick-up heads thatallow the LED dies 102 with elayers 110 to attach to the PPH 1302. Forexample, the pick-up surfaces 1304 may be glass or fused silica. Thepick-up surfaces 1304 interface with the elayer 110 of the LED dies 102using adhesion forces, such as Van der Waals. The adhesive 108 may beremoved from the carrier substrate 104 before the pick-up surfaces 1304attach to the elayer 110 of each LED die 102. Although the elayers 110discussed herein are particularly adapted for non-conformable pick-upheads, in some embodiments, the pick-up surfaces 1304 are conformable,such as with an elastomeric coating.

Subsequent to the PPH 1302 picking up the one or more first LED dies 102a with the first pick-up surface 1304 a, the PPH 1302 is rotated aboutaxis 1308 to pick up one or more second LED dies 102 b with a secondpick-up surface 1304 b of the PPH 1302. The second pick-up surface 1304b may be adjacent to the first pick-up surface 1304 a, as shown in FIG.13, or may be a non-adjacent pick-up surface 1304 to the first pick-upsurface 1304 a.

FIG. 14 is a cross sectional view of the display manufacturing system1300 during LED die 102 placement on a display substrate 1402, accordingto one embodiment. The LED dies 102 attached to the PPH 1302 via theelayers 110 are placed on the display substrate 1402 of an electronicdisplay.

After the PPH 1302 has been populated with LED dies 102, the PPH 1302 ismoved away from the carrier substrate 104 and aligned with the displaysubstrate 1402. For example, the PPH 1302 may be lifted away from thecarrier substrate 104 by the micromanipulator 1306 for subsequentplacement of the LED dies 102 on the display substrate 1402. Themicromanipulator 1306 places the LED dies 102 on the display substrate1402 by aligning the PPH 1302 with the display substrate 1402 androlling the PPH 1302 across the display substrate 1402. The displaysubstrate 1402 may be part of an electronic display with the LED dies102 placed at sub-pixel locations to connect with the control circuitsin the display substrate 1402 that drive the LED dies 102. For example,the display substrate 1402 may be a printed circuit board including gatelines and data lines for a control circuit at each sub-pixel that drivethe LED dies 102 according to signals on the gate and data lines. Afterplacement, the LED dies 102 may be bonded to the display substrate 1402,such as using thermocompression (TC) bonding.

FIG. 15 is a schematic diagram of a cross section of a mLED 1500,according to one embodiment. The mLED 1500 is an example of an LED die102 having a light emitting side 112 on which the elayer 110 is formedto facilitate adhesive attachment with a pick-up head. The mLED 1500 mayinclude, among other components, an epitaxial structure 1502 formed on agrowth substrate (not shown). The epitaxial structure 1502 includes amulti-quantum well (“MQW”) 1504. The mLED 1500 further includes adielectric layer 1506 on the epitaxial structure 1502, a p-contact 1508on the dielectric layer 1506, and an n-contact 1510 on the epitaxialstructure 1502. The epitaxial structure 1502 is shaped, such as via anetch process, into a mesa 1512 and a base 1514 of the mesa 1512. Themulti-quantum well 1504 defines an active light emitting area that isincluded in the structure of the mesa 1512. The mesa 1512 may include atruncated top defined on a side opposed to a light emitting side 112 ofthe mLED 1500.

If the semiconductor structure of the mLED 1500 is grown on a growthsubstrate, such as a non-transparent substrate, the growth substrate maybe removed to reveal the light emitting side 112 as shown in FIG. 15. Inanother example, the growth substrate is not removed, such as when thegrowth substrate is transparent for the light emitted by the mLED 1500.

The mesa 1512 may include various shapes, such as a parabolic shape witha truncated top, to form a reflective enclosure for light 1516 generatedwithin the mLED 1500. In other embodiments, the mesa 1512 may include acylindrical shape with a truncated top, or a conic shape with atruncated top. The arrows show how the light 1516 emitted from the MQW1504 is reflected off the p-contact 1508 and internal walls of the mesa1512 toward the light emitting side 112 at an angle sufficient for thelight to escape the mLED device 1500 (i.e., within a critical angle oftotal internal reflection). The p-contact 1508 and the n-contact 1510connect the mLED 1500, such as to the display substrate including acontrol circuit for the mLED 1500. The n-contact 1510 is formed at thebase 1514 on a side opposite the light emitting side 112.

The mLED 1500 may include an active light emitting area defined by theMQW 1504. The mLED 1500 directs the light 1516 from the MQW 1504 andincreases the brightness level of the light output. In particular, themesa 1512 and p-contact 1508 cause reflection of the light 1516 from theMWQ 1504 to form a collimated or quasi-collimated light beam emergingfrom the light emitting side 112.

The foregoing description of the embodiments has been presented for thepurpose of illustration; it is not intended to be exhaustive or to limitthe patent rights to the precise forms disclosed. For example, thedeposited layer may be made of other materials, and the same method canbe applied to micro-electric devices other than LEDs. Persons skilled inthe relevant art can appreciate that many modifications and variationsare possible in light of the above disclosure.

The language used in the specification has been principally selected forreadability and instructional purposes, and it may not have beenselected to delineate or circumscribe the inventive subject matter. Itis therefore intended that the scope of the patent rights be limited notby this detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thepatent rights, which is set forth in the following claims.

What is claimed is:
 1. A method, comprising: depositing a photoresistincluding an elastomeric material over and between light emitting diode(LED) dies on a carrier substrate; applying light through the carriersubstrate towards the LED dies and the deposited photoresist, the lightbeing absorbed by first portions of the photoresist between the LED diesto cause the first portions of the photoresist including firstelastomeric material to be soluble, the light being absorbed by the LEDdies to mask insoluble second portions of the photoresist includingsecond elastomeric material over the LED dies from the light; anddissolving the soluble first portions of the photoresist to remove thefirst portions of the photoresist including the first elastomericmaterial between the LED dies, the second elastomeric material over theLED dies being retained to form elastomeric interface layers over theLED dies.
 2. The method of claim 1, further comprising: picking up atleast a portion of the LED dies on the carrier substrate by attaching anon-conformable pick-up head to the elastomeric interface layers overthe LED dies; and placing the at least a portion of the LED diesattached to the non-conformable pick-up head on a display substratedefining pixel control circuits of an electronic display.
 3. The methodof claim 1, further comprising: fabricating the LED dies on a nativesubstrate; attaching a carrier film capable of expanding to a first sideof the LED dies on the native substrate; detaching the native substratefrom the LED dies; singulating the LED dies attached to the carrierfilm; separating the LED dies by expanding the carrier film to definethe open regions between the LED dies; applying the carrier substrate toa second side of the LED dies, the carrier substrate including a glasssubstrate layer and an adhesive layer, the LED dies being attached tothe adhesive layer of the carrier substrate with the open regions beingdefined between the LED dies; and separating the carrier film from thefirst side of the LED dies to expose the first side of the LED dies tothe depositing of the photoresist.
 4. The method of claim 1, furthercomprising curing the insoluble second portions of the photoresistsubsequent to removing the first portions.
 5. The method of claim 1,wherein the LED dies absorb Ultraviolet (UV) light incident on the LEDdies through the carrier substrate.
 6. The method of claim 1, whereinthe LED dies include Gallium nitride (GaN), gallium arsenide (GaAs), orgallium phosphide (GaP).
 7. The method of claim 1, wherein the LED diesare micro-LEDs or vertical-cavity surface-emitting lasers (VCSELs). 8.The method of claim 1, further comprising baking the photoresist priorto applying the light.
 9. A method, comprising: depositing a photoresistincluding an elastomeric material over and at side surfaces of a lightemitting diode (LED) die on a carrier substrate; applying light throughthe carrier substrate towards the LED die and the deposited photoresist,the light being absorbed by first portions of the photoresist at theside surfaces to cause the first portions of the photoresist includingfirst elastomeric material to be soluble, the light being absorbed bythe LED die to mask an insoluble second portion of the photoresistincluding second elastomeric material over the LED die from the light;and dissolving the soluble first portions of the photoresist to removethe first portions of the photoresist including the first elastomericmaterial at the side surfaces, the second elastomeric material over theLED die being retained to form an elastomeric interface layer over theLED die.
 10. The method of claim 9, further comprising: picking up theLED die on the carrier substrate by attaching a non-conformable pick-uphead to the elastomeric interface layer over the LED die; and placingthe LED die attached to the non-conformable pick-up head on a displaysubstrate defining pixel control circuits of an electronic display. 11.The method of claim 9, further comprising curing the insoluble secondportion of the photoresist subsequent to removing the first portions.12. The method of claim 9, wherein the LED die absorbs Ultraviolet (UV)light incident on the LED die through the carrier substrate.
 13. Themethod of claim 9, wherein the LED die includes Gallium nitride (GaN),gallium arsenide (GaAs), or gallium phosphide (GaP).
 14. The method ofclaim 9, wherein the LED die is a micro-LED or a vertical-cavitysurface-emitting laser (VCSEL).
 15. The method of claim 9, furthercomprising baking the photoresist prior to applying the light.
 16. Anelectronic display panel fabricated by a method, comprising: depositinga photoresist including an elastomeric material over and between lightemitting diode (LED) dies on a carrier substrate; applying light throughthe carrier substrate towards the LED dies and the depositedphotoresist, the light being absorbed by first portions of thephotoresist between the LED dies to cause the first portions of thephotoresist including first elastomeric material to be soluble, thelight being absorbed by the LED dies to mask insoluble second portionsof the photoresist including second elastomeric material over the LEDdies from the light; dissolving the soluble first portions of thephotoresist to remove the first portions of the photoresist includingthe first elastomeric material between the LED dies, the secondelastomeric material over the LED dies being retained to formelastomeric interface layers over the LED dies; picking up at least aportion of the LED dies on the carrier substrate by attaching anon-conformable pick-up head to the elastomeric interface layers overthe LED dies; and placing the at least a portion of the LED diesattached to the non-conformable pick-up head on a display substratedefining pixel control circuits of an electronic display.
 17. Theelectronic display panel of claim 16, further comprising: fabricatingthe LED dies on a native substrate; attaching a carrier film capable ofexpanding to a first side of the LED dies on the native substrate;detaching the native substrate from the LED dies; singulating the LEDdies attached to the carrier film; separating the LED dies by expandingthe carrier film to define the open regions between the LED dies;applying the carrier substrate to a second side of the LED dies, thecarrier substrate including a glass substrate layer and an adhesivelayer, the LED dies being attached to the adhesive layer of the carriersubstrate with the open regions being defined between the LED dies; andseparating the carrier film from the first side of the LED dies toexpose the first side of the LED dies to the depositing of thephotoresist.
 18. The method of claim 16, wherein the LED dies absorbUltraviolet (UV) light incident on the LED dies through the carriersubstrate.
 19. The electronic display panel of claim 16, wherein the LEDdies are micro-LEDs and include Gallium nitride (GaN), gallium arsenide(GaAs), or gallium phosphide (GaP).
 20. The electronic display panel ofclaim 16, further comprising baking the photoresist prior to applyingthe light.